Overview
Definition:
Post-exposure prophylaxis (PEP) for varicella-zoster virus (VZV) in siblings aims to prevent or attenuate infection after exposure to an index case of chickenpox
This typically involves administering the varicella vaccine or, in select high-risk individuals, varicella-zoster immune globulin (VZIG).
Epidemiology:
Varicella is highly contagious, with siblings of an infected child having a very high risk of transmission (up to 90%)
In India, varicella is endemic, with significant outbreaks occurring
The incidence is highest in children aged 5-10 years
Vaccination has significantly reduced disease incidence in vaccinated populations.
Clinical Significance:
Preventing varicella in susceptible siblings is crucial to avoid illness, potential complications (pneumonia, encephalitis, secondary bacterial infections), and to reduce further spread within households and communities
It is particularly important for siblings who are immunocompromised or too young to be vaccinated
This topic is frequently tested in DNB and NEET SS examinations, requiring a thorough understanding of current guidelines.
Risk Assessment And Indications
Identifying Exposure:
A sibling is considered exposed if they have had close contact with a person with confirmed or probable varicella within the contagious period (typically 1-2 days before rash onset to the crusting of all lesions).
Susceptibility Assessment:
Determine the sibling's immune status: documented history of varicella, documented vaccination with 2 doses of varicella vaccine, or serological evidence of immunity
Susceptible individuals are those without any of these criteria.
Indications For Vaccine PEP:
Varicella vaccine (live attenuated) is recommended for susceptible siblings within 72 hours (ideally 48 hours) of exposure if they are immunocompetent
It can be given up to 5 days post-exposure with some potential benefit
This aims to prevent infection or reduce severity.
Indications For VZIG:
VZIG is reserved for high-risk, susceptible individuals who cannot receive the vaccine or in whom the vaccine may be less effective
This includes immunocompromised children, neonates born to mothers with varicella around delivery, pregnant women exposed to varicella, and premature infants born at <28 weeks gestation or weighing <1000g
VZIG must be administered within 96 hours of exposure.
Management Strategies
Vaccine Administration:
For immunocompetent, susceptible siblings, administer one dose of varicella vaccine (live attenuated)
The dose is typically 0.5 mL subcutaneously
For PEP, it is usually one dose, even if the child has had one dose previously, as PEP doses may be spaced differently.
VZIG Administration:
VZIG is given intramuscularly at a dose of 125 units/10 kg body weight, with a maximum dose of 625 units
It provides passive immunity and is primarily used for prophylaxis in high-risk individuals.
Supportive Care:
Regardless of PEP, symptomatic management is crucial
This includes antipyretics (paracetamol/ibuprofen), pruritus relief (calamine lotion, oral antihistamines), and monitoring for signs of complications
Avoid aspirin due to the risk of Reye's syndrome.
Isolation Precautions:
The index case should be isolated until all lesions have crusted over
Susceptible siblings should also avoid contact with immunocompromised individuals until they have either developed immunity or recovered from any potential infection.
Vaccine Vs VZIG Considerations
Vaccine Advantages:
Induces active immunity, providing long-lasting protection
Generally well-tolerated and readily available.
Vaccine Disadvantages:
Live attenuated virus, contraindicated in severely immunocompromised individuals
Onset of protection may be slower than VZIG.
VZIG Advantages:
Provides immediate passive immunity, suitable for immunocompromised individuals
Can be effective up to 96 hours post-exposure.
VZIG Disadvantages:
Provides temporary immunity, can interfere with the response to live vaccines given concurrently or soon after
More expensive and less readily available than the vaccine
Potential for anaphylaxis (rare).
Prognosis And Follow Up
Outcomes With Vaccine PEP:
If given within 72 hours, the vaccine can prevent varicella entirely in about 50-80% of cases or significantly attenuate the disease, leading to fewer lesions and milder symptoms
A breakthrough case may still occur but is typically less severe.
Outcomes With VZIG:
VZIG can prevent or attenuate varicella in high-risk individuals, reducing the risk of severe disease and complications
It is a bridge to allow time for immune reconstitution or alternative treatments.
Monitoring For Breakthrough Infection:
Susceptible siblings who receive PEP should be monitored for the development of varicella lesions
Even with PEP, mild or atypical cases can occur.
Long Term Immunity:
The varicella vaccine provides long-term immunity, similar to that after natural infection
VZIG provides only temporary protection.
Key Points
Exam Focus:
Key decision points revolve around the timing of exposure, the sibling's immune status, and the choice between vaccine and VZIG
Understand contraindications for live vaccines
Dosing of VZIG is critical.
Clinical Pearls:
Always confirm vaccination status and previous varicella history
Prompt administration of vaccine (within 72 hours) is paramount for immunocompetent siblings
Consider immunocompromised status carefully for VZIG indication
Educate parents on isolation and monitoring.
Common Mistakes:
Delayed administration of PEP
Administering live vaccine to severely immunocompromised patients without proper consultation
Incorrect VZIG dosing or administration window
Failing to consider breakthrough infections
Not documenting previous varicella or vaccination.